Now I've done it ...
Yep, ebay again. I just couldn't resist the "Georgian Vellum Indenture 1722 Eliza Heald Lincoln".
Thirty pounds seems a reasonable price to me, not that I actually did any research on the subject; I was captivated, so I bought it. I have got an idea of how I might get the money back, but I really don't care if it works out.
Yes, an utterly frivolous purchase, but rather better than a new item of clothing, I think!
P.S. If you are thinking "that should be in a museum", well you're probably right, but my will does leave all my books to a library: that's my excuse anyway!